Marine engine exhaust systems typically inject liquid coolant into engine exhaust gas to cool the exhaust gas from the engine by forming a fluid mixture of the liquid coolant and exhaust gas. This method may also result in noise reduction and reduced pollutants in the expelled exhaust gas. The liquid coolant is typically water taken from the body of water in which the marine vessel is floating. The pollutants, such as particulate matter and unburned fuel, exit with the exhaust gas when it leaves the engine. Once the liquid coolant and exhaust gas are mixed, the resulting fluid mixture includes these pollutants. In certain exhaust systems, the fluid mixture is thereafter substantially separated into its liquid coolant and exhaust gas components. The exhaust gas and fluid may thereafter be expelled through separate conduits, after the gas/fluid separation process. This process extracts significant particulate matter and unburned fuel, such as oil, from the exhaust gas, resulting in a cleaner exhaust gas when it is released from the exhaust system. However, the particulate matter and unburned fuel remain largely in the liquid coolant and are usually discharged with the liquid coolant into the body of water in which the vessel is located. Thus, the benefit to the ecology of removing pollutants from the exhaust gas is offset by the negative ecological impact of pollutants being added to the discharged liquid coolant. For example, when the liquid coolant is jettisoned overboard, a slick of particulate matter or soot and unburned fuel may float on the surface of the water. The particulate matter eventually saturates and sinks, while the unburned fuel floats on the surface until it evaporates or until it is absorbed on the shore, such as in birds' feathers or other coalescing surfaces.
Methods for cleansing the liquid coolant to be discharged from marine engine exhaust systems include various soot sinker designs, which have the purpose of accumulating and storing floating particulate matter until it becomes water saturated. Thereafter, the sunken particulate matter is expelled from the exhaust system into the surrounding water to sink, away from visible pollution on the surface of the water. Other devices use fibrous filters and pressure pumps to remove the particulate matter and unburned fuel from the liquid coolant. In order to keep the filters functioning properly, they may need to be frequently cleaned or replaced.